In the past, membranes of the type proposed in the present invention have been provided for covering a substrate, such as a roof deck or a basement wall, to provide a waterproof coating for the substrate. Such membranes conventionally include a release paper lamina upon which is superimposed a primary lamina which is a rubber-modified asphalt of appreciable thickness. An upper lamina of a plastic film, typically polyethylene, is applied to the upper surface of the primary lamina and is bonded thereto by heat and pressure to provide a composite membrane which is generally in the form of an elongated, relatively narrow strip which is unrolled onto the surface to be covered.
It generally is necessary to apply a plurality of such strips in overlapping relation to the substrate in order to completely cover the substrate surface. In order to provide a sealed overlap, the uppermost plastic lamina does not completely cover the primary lamina. Thus, an uncovered "selvage" edge or "bead" of uncovered primary lamina is left exposed, so that the two primary lamina of adjacent strips can be brought into sealing contact when the strips are overlapped. This "bead" or "selvage" edge is generally only about 1/8 to about 1/2" wide, and it does not provide a sufficient area to ensure sealing of the two primary lamina to one another. Further, it is necessary in manufacturing the membrane to apply a narrower strip of plastic lamina to the underlying primary lamina in order to leave the "bead," and severe registration problems have occurred during manufacturing so that an inadequate bead is often provided. Also, the plastic lamina provides an additional waterproofing layer in the membrane and the presence of the "bead" results in a poor quality membrane at the overlapped portions.
The present invention provides a membrane which differs substantially from those in the prior art and which possesses several attributes missing from the prior art. In the present invention, the primary lamina and the plastic covering lamina are coextensive so that the entire surface of the primary lamina is covered with the plastic film lamina. Consequently, there are no problems of registration during manufacture, and the membrane has uniform waterproofing properties and other properties throughout its entire extent.
In accordance with the present invention, one or more edges of the uppermost plastic lamina bear a layer of asphalt-based adhesive which is of substantially greater width, i.e., on the order of at least 1/2 inch and preferably from 11/2 to 3 inches, in width, to accommodate substantial overlapping between adjacent strips and to provide a substantially improved seal between the adjacent strips.
The specific adhesive composition which is utilized on the plastic film is an important aspect of the present invention. This adhesive must adhere firmly to the plastic film, typically a polyethylene film, and it also must retain the overlapping primary lamina in position. Preferably, this adhesive is a composition of the type disclosed in our co-pending application U.S. Pat. No. 4,654,385, filed in the United States Patent and Trademark Office on Dec. 30, 1985, and incorporated herein by reference. The adhesive generally is an aqueous emulsion of a chemically modified asphalt and non-modified asphalt emulsified in an emulsion medium which comprises water plus a surfactant. It has been found that such an emulsion adhesive results in excellent adherence to the plastic film of the membrane, firmly adheres to the overlapping primary lamina, and the emulsion is non-toxic and environmentally safe since it contains no organic solvents.